Hi Jonathan, On 25. 03. 24 09:32, Andrej Picej wrote: > Hi Jonathan, > > On 24. 03. 24 14:55, Jonathan Cameron wrote: >> On Wed, 20 Mar 2024 11:04:04 +0100 >> Andrej Picej <andrej.picej@xxxxxxxxx> wrote: >> >>> Hi all, >>> >>> we had some problems with failing ADC calibration on the i.MX93 boards. >>> Changing default calibration settings fixed this. The board where this >>> patches are useful is not yet upstream but will be soon (hopefully). >> >> Tell us more. My initial instinct is that this shouldn't be board >> specific. >> What's the trade off we are making here? Time vs precision of >> calibration or >> something else? If these are set to a level by default that doesn't work >> for our board, maybe we should just change them for all devices? >> The imx93_adc driver is quite new. If you look at line #162, you will find a comment by the original author: > /* > * TODO: we use the default TSAMP/NRSMPL/AVGEN in MCR, > * can add the setting of these bit if need in future. > */ URL: https://github.com/torvalds/linux/blob/master/drivers/iio/adc/imx93_adc.c#L162 So, for most use-cases the default setting should work, but why not make them configurable? So this patch-series just implement what was missing from the beginning / was planned for later. BR, Primoz > > So we have two different boards with the same SoC. On one, the > calibration works with the default values, on the second one the > calibration fails, which makes the ADC unusable. What the ADC lines > measure differ between the boards though. But the implementation is > nothing out of the ordinary. > > We tried different things but the only thing that helped is to use > different calibration properties. We tried deferring the probe and > calibration until later boot and after boot, but it did not help. > > In the Reference Manual [1] (chapter 72.5.1) it is written: > >> 4. Configure desired calibration settings (default values kept for >> highest accuracy maximum time). > > So your assumption is correct, longer calibration time (more averaging > samples) -> higher precision. The default values go for a high accuracy. > And since we use a NRSMPL (Number of Averaging Samples) of 32 instead of > default 512, we reduce the accuracy so the calibration values pass the > internal defined limits. > > I'm not sure that changing default values is the right solution here. We > saw default values work with one of the boards. And since the NXP kept > these values adjustable I think there is a reason behind it. > > Note: When I say one of the boards I mean one board form. So same board > version, but different HW. > > Best regards, > Andrej > > [1] i.MX 93 Applications Processor Reference Manual, Rev. 4, 12/2023 > _______________________________________________ > upstream mailing list > upstream@xxxxxxxxxxxxxxx > http://lists.phytec.de/cgi-bin/mailman/listinfo/upstream
